JP5982255B2 - Gradient magnetic field power supply device and gradient magnetic field power supply control program - Google Patents

Description

  The present invention relates to a gradient magnetic field power supply device applied to an MRI (magnetic resonance imaging) apparatus.

  In the gradient magnetic field power supply device applied to the MRI apparatus, the gradient magnetic field coil that generates the gradient magnetic field is applied with a high voltage to improve the change response of the gradient magnetic field.

As means for applying a high voltage to the gradient magnetic field coil, a circuit configuration using high-voltage components or a high voltage configuration by increasing the number of inverter stages is applied.

  A circuit configuration using high-voltage components may be disadvantageous in terms of economy because the components are expensive.

On the other hand, in the high voltage configuration by accumulating the number of inverter stages, the number of switching elements increases with the number of inverter stages, and the switching loss also increases in proportion to the number of operating switching elements, so the required output voltage changes dynamically. In such an operation, since the operation status of the device is not always the maximum load (maximum performance), there is an operation status where the performance of the device is excessive with respect to the required responsiveness, and the inverter circuit that becomes redundant at that time also performs switching operation Therefore, a switching loss that does not contribute to the output causes a reduction in power efficiency.

  As a prior art in which a power amplifier circuit is configured in multiple stages, a high-frequency power device that switches the number of amplification stages according to the output power of a modulated signal to be amplified (see cited document 1), a low power mode among the first and second amplifiers At that time, there was a linear power amplifier (see the cited document 2) that operates only the first amplifier by bias-controlling the second amplifier to the OFF state.

JP 2011-120142 A Special table 2006-50083 gazette

  The problem to be solved by the present invention is to provide a gradient magnetic field power supply device in which a switching loss is reduced in a gradient magnetic field power supply configuration by increasing the number of inverter stages.

  The gradient magnetic field power supply device of the embodiment controls an inverter unit having a multi-stage inverter block that outputs a voltage supplied to the gradient magnetic field coil, and a gradient magnetic field power source supplied to the gradient coil by controlling the inverter unit And a switching means for switchingly connecting a predetermined block in a fixed order from the multi-stage inverter block between the power supply output terminals for outputting the voltage. And the controller determines whether to increase / decrease the gradient per unit time based on the gradient of the target gradient coil current waveform, and controls the switch means according to the increase / decrease determination to switch the number of inverter stages. And a processing means for stopping the supply of the switching control signal to the separated inverter block. To.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows the structure of the MRI apparatus which can apply the gradient magnetic field power supply device which concerns on embodiment of this invention. The block diagram which shows the structural example of the said gradient magnetic field power supply device. The circuit diagram which shows the circuit structural example of the said gradient magnetic field power supply device. The flowchart which shows the control processing procedure of the said gradient magnetic field power supply device. Operation | movement explanatory drawing for demonstrating the control example of the gradient magnetic field current waveform of the said gradient magnetic field power supply device. The timing chart which shows the example of control of the gradient magnetic field current waveform of the said gradient magnetic field power supply device.

  The responsiveness that is one of the characteristics in the specifications of the gradient magnetic field power supply device depends on the voltage applied to the gradient magnetic field coil. Therefore, how to apply a higher voltage to the gradient magnetic field coil is an issue for improving the responsiveness. Become. In the design of specifications with high responsiveness, a configuration is adopted in which a high voltage can be applied to the gradient magnetic field coil, but as a specific realization method, as described above, in addition to a method using many high-voltage elements, an inverter It is also possible to increase the number of stages to increase the voltage and increase the voltage. In any of these implementation methods, a specification that does not require high responsiveness causes an increase in the cost of the device, and at present, an individual system or device is individually designed according to the required performance. When adopting an implementation method that increases the number of inverter stages, the number of inverter stages required for high voltage application increases in a device configuration that requires high responsiveness, which inevitably increases the switching loss due to inverter circuit elements, and depends on the operating conditions. Is a factor that reduces power efficiency.

  In this embodiment, by adopting an implementation method that increases the number of inverter stages in which the specification-specific dependency part at the circuit level is relatively limited and adopting a circuit configuration that changes the number of inverter stages according to the device level, the individual design burden The system cost and maintenance burden are reduced, and highly efficient operation is possible. In order to realize this function, in the control unit that controls the inverter unit in which inverter blocks are stacked, the number of inverter stages in the inverter unit is dynamically increased or decreased according to the operation status of the device. As a result, the switching operation of the inverter stage (inverter block) removed from the stack is stopped. As described above, in the apparatus operation stage, the number of stages of the inverter block is dynamically controlled according to the operation state (maximum / steady state, etc.), and the switching of the inverter stage number is dynamically stopped according to the operation state, thereby improving the responsiveness. It is possible to achieve both high efficiency operation. The required number of inverter stages varies depending on the load to be controlled and the required operating conditions, but by adopting the inverter stage stacking method, the number of inverter stages can be increased or decreased to meet the target specifications without changing the basic structure of the equipment. It becomes possible. In addition, when switching of the inverter stage number is dynamically stopped according to the operation situation, a situation occurs in which an extra inverter stage number that does not contribute to output occurs following the change in the operation situation (required performance) Switching loss in the inverter block can be reduced.

  Embodiments of the present invention will be described below with reference to the drawings. In this embodiment, the gradient magnetic field power supply device is represented as “G-AMP” and the gradient coil is represented as “G coil” in the drawing.

  FIG. 1 shows a schematic configuration of an MRI apparatus to which the gradient magnetic field power supply device (G-AMP) according to this embodiment can be applied, and FIG. 2 shows a configuration example of the gradient magnetic field power supply device. FIG. 3 shows a basic circuit configuration example.

  As shown in FIG. 1, the MRI apparatus is a control target of a gradient magnetic field power supply (G-AMP) 1, a radio wave transmission unit 2, a radio wave reception unit 3, a host device 4, and a host device 4. A coil (L). The coil (L) includes a gradient magnetic field coil (G coil; La), an RF coil (Lb), and a static magnetic field coil (Lc) to be controlled in this embodiment.

  The host device 4 sets a target value for obtaining a desired gradient magnetic field for the gradient magnetic field power supply device (G-AMP) 1. The gradient magnetic field power supply device (G-AMP) 1 generates, for example, a voltage for generating a current waveform as shown in FIGS. 5 and 6 based on the target value set by the host device 4, and the gradient magnetic field coil ( To La). Here, description of power supply to the static magnetic field coil (Lc) and radio wave (RF) transmission / reception operations (operations of the radio wave transmission unit 2 and the radio wave reception unit 3) are omitted.

  As shown in FIG. 2, a gradient magnetic field power supply device (G-AMP) 1 according to an embodiment of the present invention includes an inverter unit 11 having inverter blocks 12a, 12b,..., 12n configured in multiple stages (n stages). The inverter blocks 12a, 12b,... Of the inverter unit 11 based on the target value (IP) given from the host device 4 and the feedback value (IF) of the gradient magnetic field power supply current in the gradient coil (La). And a control unit 10 for controlling 12n.

  The inverter unit 11 has an inverter output terminal (DT-P) on the P (positive) side in the first-stage inverter block 12a which is the uppermost stage among the inverter blocks stacked in multiple stages, and is the lowermost stage. The n-th inverter block 12n has an N (negative) inverter output terminal (DT-N), and the voltage output from the inverter output terminal (DT-P, DT-N) is applied to the gradient magnetic field coil. (La). Further, the inverter unit 11 switches between the inverter output terminals (DT-P, DT-N) and switches 13, 13, 13 for switching and connecting the multi-stage inverter blocks so as to be detachable in a certain order for each stage. ....

  The control unit 10 performs increase / decrease determination of the gradient per unit time based on the gradient of the target gradient magnetic field coil current waveform, generates an inverter block control signal (BC) according to the increase / decrease determination, and generates the inverter block control signal (BC) according to the control signal. The switching means 13, 13... Are turned on / off to perform switching connection of the number of inverter stages (connection / disconnection of stacked inverter blocks), and supply of a switching control signal (GC) to the disconnected inverter block. Processing means for stopping is provided. The processing procedure of this processing means will be described later with reference to FIG.

  FIG. 3 shows a circuit configuration of the gradient magnetic field power supply device (G-AMP) 1 in the embodiment. Here, in order to simplify the description, a configuration of an inverter unit in which three stages of inverter blocks are stacked (n = 3) is illustrated. Here, among the inverter blocks stacked in multiple stages (three stages), the first-stage inverter block 12a, which is the uppermost stage, has a P-side inverter output terminal (DT-P), and the third stage that is the lowermost stage. The inverter block 12c at the stage has an inverter output terminal (DT-N) on the N side, and the operating DC power supplies (PS (+), PS (-)) are individually provided for each inverter block (for each stage). Supplied and applied.

  In the inverter configuration in which the inverter blocks are stacked in three stages, switch means connected in cascade between each stage of the first-stage inverter block 12a as the uppermost stage and the third-stage inverter block 12c as the lowermost stage. 13 (1) and 13 (2) are provided. Here, the switch means 13 (1) is connected between the N-side output terminals of the first stage inverter block 12a and the second stage inverter block 12b, and the switch means 13 (2) is the second stage inverter. Connected between the N side output terminals of the block 12b and the third stage inverter block 12c, the common terminal (COM) of the switch means 13 (1) is connected to the OFF side switching contact of the switch means 13 (2), The common terminal (COM) of the switch means 13 (2) is connected to the N-side inverter output terminal (DT-N).

  The switch means 13 (1) is ON / OFF controlled by the inverter block control signal (BC-1) output from the control unit 10, and when in the switch ON state, the first stage inverter block 12a which is the uppermost stage. When the inverter block 12b which is the second stage (middle stage) is connected and is in the switch-off state, a short circuit is formed in the second stage inverter block 12b, and the inverter block 12b is separated from the stacked stage. The inverter block 12b is removed from the power amplification stage loaded in the inverter unit 11. In synchronization with this disconnection timing, the control unit 10 stops supplying the switching control signals (GC: GC-A2a, GC-A2b, GC-B2a, GC-B2b) to the disconnected inverter block 12b.

  The switch means 13 (2) is ON / OFF controlled by the inverter block control signal (BC-2) output from the control unit 10, and when in the switch ON state, the switch means 13 (2) is connected to the second stage inverter block 12b which is the middle stage. When the third-stage inverter block 12c, which is the lowest stage, is stacked and in the switch-off state, a short circuit is formed in the third-stage inverter block 12c, and the inverter block 12c is disconnected from the stacked stage, The block 12c is removed from the power amplification stage stacked in the inverter unit 11. In synchronization with this disconnection timing, the control unit 10 stops supplying the switching control signals (GC: GC-A3a, GC-A3b, GC-B3a, GC-B3b) to the disconnected inverter block 12c.

  Accordingly, when both the switch means 13 (1) and the switch means 13 (2) are in the switch-on state, all three stages of inverter blocks 12a, 12b, 12c are stacked on the inverter unit 11, and the inverter output terminal (DT -P, DT-N) outputs a high voltage by stacking three stages.

  When only the switch means 13 (1) is in the switch-on state among the switch means 13 (1) and 13 (2), the third-stage inverter block 12c, which is the lowest stage, is disconnected from the stacked stage. Thus, a voltage obtained by stacking two stages is output from the inverter output terminal (DT-P, DT-N).

  When both the switch means 13 (1) and 13 (2) are in the switch-off state, the inverter blocks 12b and 12c are both disconnected from the stacked stage, and the inverter output terminals (DT-P, DT-N) A low voltage for only one stage is output. In each stage number connection, between the inverter output terminals (DT-P, DT-N), there is a current path from the P side to the N side via the gradient magnetic field coil (La) and a power path in the opposite direction. It is formed alternately.

  FIG. 4 shows a control processing procedure in the control unit 10 of the above-described gradient magnetic field power supply device (G-AMP) 1, and FIGS. 5 and 6 show control examples of the gradient magnetic field current waveform of the device.

  The control unit 10 performs the increase / decrease determination of the gradient per unit time based on the gradient of the target gradient magnetic field coil current waveform according to the target value given from the host device 4 according to the processing procedure shown in FIG. In accordance with the increase / decrease determination, the switching means 13 is controlled to perform switching connection of the number of inverter stages, and processing for stopping the supply of the switching control signal to the disconnected inverter block is performed. This processing operation will be described with reference to FIGS.

  A target value for obtaining a gradient magnetic field desired by the MRI system is notified from the host device 4 to the gradient magnetic field power supply device (G-AMP) 1. The format of the target value varies depending on the system. Here, a case where the gradient coil current waveform is transmitted as the target value will be described as an example.

  The control unit 10 monitors the operation state related to the gradient magnetic field power supply, and when a surplus occurs in the number of inverter stages, the control unit 10 dynamically stops the switching of the inverter circuit, so that the operation state (required performance) at that time is changed. It implements a control processing function that tracks changes and reduces switching loss.

  When the control unit 10 receives the target value (step S11), the control unit 10 calculates the gradient (di / dt) of the received target value from the difference information between the target value before unit sampling and the current target value (step S11). S12). An example of this calculation is shown in FIG.

  From the magnitude and direction of the gradient (di / dt) of the target value calculated here, the applied voltage to the gradient magnetic field coil (La) is determined (steps S12 and S13). In this determination, it is determined whether or not the magnitude of the target value inclination (di / dt) is within a preset threshold value range, and the magnitude of the target value inclination (di / dt) exceeds the threshold value. When it is, it is determined whether the inclination is an increasing direction or a decreasing direction. Here, when the magnitude of the slope is in the increasing direction exceeding the threshold, the increase in the number of inverter stages is determined by determining the slope increase, and when the magnitude of the slope is in the decreasing direction exceeding the threshold, If the inclination reduction is determined and the inverter stage number is reduced, and the magnitude of the slope is within the threshold range, the inverter stage number is not increased or the inverter stage number is not reduced. An example of this determination is shown in FIG.

  In the determination of the applied voltage to the gradient magnetic field coil (La) (step S13), the control unit 10 performs the process of increasing the number of inverter stages when determining the increase in inclination, and FIG. 6 (b) and FIG. 6 (c). As shown in FIG. 2, the inverter block control signal (BC-1) and the inverter block control signal (BC-2) are respectively switched on, and the switch means 13 (1) and the switch means 13 (2) are respectively switched on. Further, in synchronization with this switch-on timing, as shown in FIGS. 6D to 6F, switching control signals (GC: GC-A1a, GC-A1b, GC-B1a, GC-) to the inverter block 12a. B1b) and switching control signals (GC: GC-A2a, GC-A2b, GC-B2a) to the inverter block 12b GC-B2b) and switching control signals to the inverter block 12c (GC: GC-A3a, supplies GC-A3b, GC-B3a, GC-B3b) and respectively (step S13a). As a result, all three inverter blocks 12a, 12b, 12c of the inverter unit 11 operate as power amplification stages, and are indicated by “high” in FIG. 6 (g) from the inverter output terminals (DT-P, DT-N). The maximum voltage obtained by stacking three stages is output.

  Thereafter, in the determination of the voltage applied to the gradient magnetic field coil (La) (step S13), if the magnitude of the inclination falls within the threshold range and it is determined that the inclination is reduced, the results shown in FIGS. 6B and 6C are obtained. As shown, the inverter block control signal (BC-1) and the inverter block control signal (BC-2) are set to the switch-off level, the switch means 13 (1) and the switch means 13 (2) are turned off, Further, in synchronization with the switch-off timing, as shown in FIGS. 6D to 6F, switching control signals (GC: GC-A2a, GC-A2b, GC-B2a, GC-B2b) to the inverter block 12b are used. ) And switching control signals (GC: GC-A3a, GC-A3b, GC-B3a) to the inverter block 12c GC-B3b) stops supplying the respective (step S13b). As a result, the inverter blocks 12b and 12c are both separated from the stacked stage, and the inverter output terminals (DT-P and DT-N) are separated from the inverter output terminals (DT-P and DT-N) by one stage (maximum) shown in FIG. The minimum voltage from only the upper stage is output.

  Thereafter, in the determination of the applied voltage to the gradient magnetic field coil (La) (step S13), when it is determined that the inclination is increased, as shown in FIG. 6B and FIG. 6C, the inverter block control signal (BC− 1) Of the inverter block control signal (BC-2), only the inverter block control signal (BC-1) is set to the switch-on level, the switch means 13 (1) is switched on, and further synchronized with this switch-on timing. Then, as shown in FIGS. 6D to 6F, the supply of the switching control signals (GC: GC-A2a, GC-A2b, GC-B2a, GC-B2b) to the inverter block 12b is resumed ( Step S13a). As a result, the inverter unit 11 has an amplification stage configuration of two stages by the inverter blocks 12a and 12b from which the third-stage inverter block 12c that is the lowest stage is separated, and the inverter output terminals (DT-P and DT-N). From FIG. 6 (g), a voltage obtained by stacking two stages is output.

  According to the embodiment described above, it is possible to dynamically start / stop the inverter block according to the voltage required for the gradient magnetic field coil current waveform generation required in the MRI system, thereby reducing the switching loss of the inverter unit. It can be minimized.

  In addition, according to the performance requirements of the MRI system to be built, it is possible to easily obtain the desired response performance by stacking inverter blocks with a single configuration based on general-purpose circuits, eliminating unnecessary power consumption. Thus, it is possible to construct an MRI system with excellent economic efficiency in a short period of time and to reduce the system cost.

  The above-described embodiments are presented as examples, and are not intended to limit the scope of the invention. The presented embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention.

  DESCRIPTION OF SYMBOLS 1 ... Gradient magnetic field power supply device (G-AMP), 4 ... Host apparatus, 10 ... Control part, 11 ... Inverter part, 12 (12a, 12b, ..., 12n) ... Inverter block, 13 (13 (1), 13 ( 2)) ... switch means, DT-P, DT-N ... inverter output terminal, La ... gradient magnetic field coil (G coil).

Claims (5)

In a gradient magnetic field power supply apparatus comprising an inverter unit having an inverter block configured in multiple stages, and a control unit that controls the inverter block and outputs a voltage supplied from the inverter unit to a gradient coil.
The inverter unit is
Between power supply output terminals for outputting a voltage to be supplied to the gradient magnetic field coil, comprising switch means for switching connection so that a predetermined block can be disconnected in a predetermined order from the multi-stage inverter block,
The controller is
Based on the gradient of the target gradient magnetic field coil current waveform, the inclination per unit time is determined to increase / decrease, and according to the increase / decrease determination, the switch means is controlled to perform the switching connection of the number of inverter stages, and the disconnected inverter A gradient magnetic field power supply apparatus comprising processing means for stopping supply of a switching control signal to a block.   The processing means of the control unit implements connection and disconnection processing of the inverter block, wherein the inclination of the target value increases or decreases the configuration of the inverter unit according to a preset threshold in the inclination increase / decrease determination. The gradient magnetic field power supply device according to claim 1, wherein   The gradient magnetic field power supply device according to claim 1, wherein each of the inverter blocks configured in multiple stages is configured by a single circuit module.   The processing means of the control unit is configured to output the maximum voltage of all the stacked stages of the inverter blocks configured in multiple stages when the gradient of the current waveform of the gradient magnetic field coil that requires high responsiveness is large. 2. The process according to claim 1, wherein when the gradient of the current waveform of the gradient magnetic field coil that improves responsiveness and high responsiveness is not required is small, the number of stages to be stacked is reduced to reduce switching loss. The gradient magnetic field power supply device described. A gradient magnetic field power supply control program for causing a computer to function as a control device that controls an inverter unit having a multi-stage inverter block and supplies a voltage output from the inverter unit to a gradient coil,
A function that performs increase / decrease determination of the gradient per unit time based on the gradient of the target gradient magnetic field coil current waveform,
A function of stacking the inverter blocks in multiple stages when it is determined that the slope is increasing beyond a preset threshold range;
A function of switching the inverter block to the minimum number of stages required to achieve the required responsiveness when determining a state in which the slope is within a threshold range;
A function of reducing the number of stacked stages of the inverter block when determining a state in which the slope is decreasing beyond a preset threshold range;
Gradient magnetic field power supply control program for realizing computer.

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